Shale oil boom goes bust as expected production dips for first time in years

The U.S. shale oil boom that powered the country’s highest crude oil production levels in decades appears to be slowing down due, in part, to a glut of supplies.

Oil output from the most productive U.S. shale fields is expected to drop off next month by 57,000 barrels of crude daily from April to May, the U.S. Energy Information Administration said Monday. That would represent the first monthly decline in more than four years, according to Reuters.

The EIA forecasted that the seven shale formations — Bakken, Eagle Ford, Haynesville, Marcellus, Niobrara, Permian and Utica — will produce a total of 5.56 million barrels of crude oil daily next month, down from 5.62 million barrels per day in April. While the most productive formation, Permian, will see slightly higher output — by 11,000 barrels per day, to 1.99 million — output at the next-highest producer, Eagle Ford, will drop 33,000 barrels daily while Bakken’s output will decline by 23,000 barrels next month.

(Fortune magazine recently wrote about oil boomtowns in North Dakota’s Bakken region, where the local economy is already feeling the effects of lower oil prices and could face a devastating blow if output there tails off considerably.)

In recent years, an oil boom in shale country helped U.S. crude production hit its highest levels in four decades. The seven regions accounted for 95% of domestic oil production growth between 2011 and 2013, according to the EIA.